Py4J - Multiple GatewayServer and CallbackServer instances

README.md

Py4J Multiple GatewayServer and CallbackServer instances

Compile and run TestApplication.java with py4j.jar in your classpath.

Then execute python3 test.py

Explanations

This creates three pairs of GatewayServer and CallbackServer with different ports on both the Java and Python sides. Python is driving the communication by asking Java to print a String. Then it calls a method that calls back a Python instance. Finally, it shuts down the Java GatewayServer. When the three GatewayServer instances are shut down, the Java and the Python programs exit.

test.py

from functools import partial
from threading import Thread

from py4j.java_gateway import (
    JavaGateway, GatewayParameters, CallbackServerParameters)


class IHelloImpl(object):
    def sayHello(self, i=None, s=None):
        if i is None:
            return "This is Hello!"
        else:
            return "This is Hello;\n{0}{1}".format(i, s)

    class Java:
        implements = ["py4j.examples.IHello"]


def build_gateway(java_port, python_port):
    gateway_parameters = GatewayParameters(port=java_port)
    callback_server_parameters = CallbackServerParameters(
        port=python_port)
    gateway = JavaGateway(
        gateway_parameters=gateway_parameters,
        callback_server_parameters=callback_server_parameters)
    return gateway


def execute(gateway, name):
    gateway.jvm.System.out.println("Hello from {0}".format(name))
    example = gateway.jvm.py4j.examples.ExampleClass()
    hello = IHelloImpl()
    output = example.callHello(hello);
    print(output)
    gateway.shutdown();


def main():
    gateway1 = build_gateway(10001, 10002)
    gateway2 = build_gateway(10003, 10004)
    gateway3 = build_gateway(10005, 10006)
    execute1 = partial(execute, gateway1, "gateway1")
    execute2 = partial(execute, gateway2, "gateway2")
    execute3 = partial(execute, gateway3, "gateway3")
    t1 = Thread(target=execute1)
    t2 = Thread(target=execute2)
    t3 = Thread(target=execute3)
    t1.start()
    t2.start()
    t3.start()


if __name__ == "__main__":
    main()

TestApplication.java

package py4j;

import java.net.InetAddress;

public class TestApplication {

	public static void main(String[] args) {
		try {
			GatewayServer server1 = new GatewayServer.GatewayServerBuilder()
					.javaPort(10001)
					.javaAddress(InetAddress.getByName("127.0.0.1"))
					.callbackClient(10002, InetAddress.getByName("127.0.0.1"))
					.build();
			GatewayServer server2 = new GatewayServer.GatewayServerBuilder()
					.javaPort(10003)
					.javaAddress(InetAddress.getByName("127.0.0.1"))
					.callbackClient(10004, InetAddress.getByName("127.0.0.1"))
					.build();
			GatewayServer server3 = new GatewayServer.GatewayServerBuilder()
					.javaPort(10005)
					.javaAddress(InetAddress.getByName("127.0.0.1"))
					.callbackClient(10006, InetAddress.getByName("127.0.0.1"))
					.build();
			server1.start();
			server2.start();
			server3.start();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}